Industrial developments over the last 20 years in the field of intermediates for producing plactics and synthetic fibers have led to studies of processes and catalysts for oxidizing olefins, and in particular for the oxidation of propylene to acrolein and acrylonitrile. In view of the large capacities of industrial plants where these types of oxidative reactions are carried out, it is strongly desired to obtain conversions as high as possible, either for economic reasons (even a slightly higher conversion can result in significantly increased profits) or for environmental reasons (reduced byproducts require less effort to eliminate and also reduce environmental pollution). A further important consideration relates to industrial catalysts' mechanical stability and ruggedness, particularly abrasion resistance which is an important consideration when using catalysts in fluidized beds.
Many oxidation and ammoxidation catalysts have been described in the patent literature. U.S. Pat. No. 2,904,580 discloses a catalyst composed mainly of bismuth phosphomolybdate. U.S. Pat. No. 3,198,750 discloses a catalyst composed mainly of oxides of Sb and U. Italian Pat. No. 682,880 discloses a catalyst comprising Ce, Mo and Te oxides. Additional oxidation and ammoxidation Fe and Sb oxide-based catalysts are known, such as those described in Japanese P No. 420,264, U.K. Pat. No. 983,755 and U.S. Pat. No. 3,197,419. It is also known that adding particular promoters to such catalysts provides improved yields in the ammoxidation of propylene as described, for example, in U.S. Pat. Nos. 3,338,952 and 3,546,138 wherein 30 different elements are presented as suitable promoters of Fe and Sb oxide-based catalysts when the amount of promoters is in the range of 1 to 10%. The catalysts can be used as such or supported on alumina, silica, titanium dioxide, zirconium dioxide, and the like. For example, U.K. Pat. No. 1,492,115 claims an Fe-Sb oxide-based catalyst which is promoted with other elements and which may be used either as such or supported, preferentially on silica.
However, these known catalysts have generally been found not to be entirely satisfactory with respect to one or more characteristics such as acrylonitrile yield, mechanical resistance when employed in fluidized beds, cost, procedure for preparing the catalyst, and stability with respect to long term catalytic activity and selectivity.